The present invention relates to a plasma processing apparatus and method for supplying high-frequency power to antennas to generate an electric field, causing the electric field to generate a plasma and using the plasma to process specimens.
In a plasma processing apparatus which generates plasma in a vacuum processing chamber by supplying a high-frequency current to a coil-shaped antenna to generate an electric field, causing the electric field to generate a plasma, and using the plasma for processing, if the electric field generated by the coil-shaped antenna is strong, byproducts are hardly deposited on the inner wall of the vacuum chamber by the resulting high-density plasma. On the other hand, if the electric field is weak, the density of the resulting plasma is low, and byproducts are easily deposited on the inner wall of the chamber. Such a deposit is not desirable.
One method of solving this kind of problem has been disclosed in Japanese Non-examined Patent Publication No. 8-316210 (1996). The proposed method comprises the steps of providing a high-frequency antenna which can carry a high frequency current around the outer dielectric wall of a vacuum chamber, providing an electrode which forms a uniform electric field on the inner surface of the dielectric material between this high-frequency antenna and the dielectric member to electrostatically connect the electrode with a plasma, connecting the high-frequency antenna and the electrode in parallel, supplying a small power to the electrode during plasma processing, and supplying a great power to the electrode at a break in the processing to clean the inside of the chamber.
Further, a plasma processing method has been disclosed in U.S. Pat. No. 5,811,022, which comprises the steps of providing a divided Faraday shield between the vacuum chamber and an induction coil to which a high-frequency power is applied, selecting the divided Faraday shield, and controlling the level of a plasma potential change.
The method described in the aforementioned Japanese patent employs a method of individually performing wafer processing and a cleaning process for cleaning the inside of the vacuum chamber. However, this method does not consider the throughput. Further, in this processing method, when a current flowing through an electrostatically capacitance-coupled electrode (or electrostatic capacitive coupling antenna) is made greater in a circuit having the high-frequency antenna and the electrode, which are connected in parallel, to prevent byproducts from being deposited on the inner surface of the vacuum chamber during plasma processing, the high-frequency impedances of the high-frequency antenna (inductive) and the electrode (capacitive) may not be matched. This is because the electrostatically capacitance-coupled electrode, which is provided to produce an electrostatic-coupling discharge in the circuit, works as an electric capacitor, and the high-frequency antenna, which is provided to produce an inductive coupling discharge, works as a coil. Consequently, this circuit forms a parallel resonance (which increases the combined impedance infinitely) and prevents impedance matching. Therefore, plasma processing is not available under conditions which may cause a parallel resonance, which restricts the plasma processing conditions.
Another possible problem of this processing method is that, when a current flowing through an electrostatically capacitance-coupled electrode (or electrostatic capacitive coupling antenna) is made greater to prevent byproducts from being deposited on the inner surface of the vacuum chamber during plasma processing, a great plasma by electrostatic capacitance discharge occurs, which greatly changes the plasma distribution and the uniform wafer processing condition.
In the method described in the aforementioned U.S. patent, the Faraday shield is capacitively coupled with the induction coil. In other words, when the Faraday shield is assumed to be an electrostatically-coupled electrode, the voltage applied to the electrode may be affected by the precision of re-installation of the induction coil and the electrode after the vacuum chamber is opened to the air, since the circuit for supplying a voltage to the electrode uses a floating capacitance. This floating capacitance must be increased to supply a higher voltage to the electrode. For this purpose, it is required to increase the area of the induction coil and bring the induction coil closer to the electrode. This area expansion means provision of a bigger high-voltage section and the shorter distance between the antenna or coil and the electrode may increase the possibility that abnormal discharges will be generated, which reduces the safety and reliability of the equipment. Therefore, it is not preferable to increase the voltage for the electrode so high in a system using a floating capacitance.
Meanwhile, a plasma processing apparatus of the magnetic-field plasma type can control the distribution of plasma by varying the magnetic field which is generated by an electromagnet or the like and is fit for uniform wafer processing with less deposition of byproducts. On the other hand, a plasma processing apparatus of the inductive discharge plasma type using no magnetic field has a limited means to control the plasma distribution. For example, this type of plasma processing apparatus controls the distribution of plasma by changing the shape of the vacuum chamber or adjusting the location of the inductive coupling antenna. Further, any change in a process condition may affect the plasma distribution, and a single plasma processing apparatus can perform processing only under a limited condition.
An object of the present invention is to provide a plasma processing apparatus and method which can easily control the plasma distribution in plasma processing using an inductive coupling antenna.
Another object of the present invention is to provide a plasma processing apparatus and a method thereof which can suppress deposition of byproducts on the inner wall of the vacuum chamber during plasma processing of a specimen using an inductive coupling antenna.
The aforesaid first problem can be accomplished by using an apparatus comprising an inductive coupling antenna for a wall enclosing a plasma generating area, an electrostatic capacitive coupling antenna at least for a surface which is not equipped with said inductive coupling antenna, which is electrically connected in series with the electrostatic capacitive coupling antenna, and a means for controlling the ratio of high-frequency currents flowing through said electrostatic capacitive coupling antenna and said inductive coupling antenna by controlling the ratio of high-frequency currents flowing through the inductive coupling antenna and the electrostatic capacitive coupling antenna, which are electrically connected in series, generating a plasma in the vacuum chamber with the electric field using said inductive coupling antenna and the electrostatic capacitive coupling antenna, and using said plasma to process a specimen.
The aforesaid second problem can be accomplished by using an apparatus comprising an inductive coupling antenna for a wall enclosing a plasma generating area, an electrostatic capacitive coupling antenna for a surface which is not equipped with said inductive coupling antenna, which is electrically connected in series with the electrostatic capacitive coupling antenna, and by generating an electric field using the inductive coupling antenna and the electrostatic capacitive coupling antenna, which are electrically connected in series, adding an electric field produced by the inductive coupling antenna to an area which has a very weak electric field, generating a plasma in the vacuum chamber by these electric fields, and using said plasma to process a specimen.
The plasma processing apparatus of the present invention can control the ratio of high-frequency currents flowing through inductive coupling and electrostatic capacitive coupling antennas which are electrically, connected in series to adjust the magnitudes of electric fields produced by said antennas. The present invention has an effect of enabling production of an optimum plasma in the vacuum chamber and suppressing deposition of byproducts on the inner wall of the vacuum chamber during plasma processing of wafers by inductive coupling antennas.